In the art of roll forming sheet metal, it has for many years been considered desirable to emboss transverse indentations across a strip passing along a sheet metal rolling line, or across a part of the strip, so as to provide increased strength, or to provide for a specific function in an end product. The provision of transverse indentations, coupled with the formation of longitudinal indentations or formations, in a sheet metal strip, greatly increases the rigidity of the strip, and such increase in rigidity leads to various economies, principally due to the fact that a lighter gauge of metal may be used for specific applications than was hitherto possible. For example, in the manufacture of roof decking, sheet metal having a combination of transverse indentations and longitudinal indentations is found to have much greater rigidity and thereby permits the use of lighter gauge steel, thereby making the roof decking somewhat cheaper. In addition, the use of lighter weight material permits the use of somewhat lighter gauge beams in the roof, and other supports in the building structure which thereby permits considerable savings in construction costs over conventional materials.
However, notwithstanding the desirability of such products, progress in the development of manufacturing techniques for such products in the past has been disappointing. Various proposals have been put forward for manufacturing these types of products.
For example, U.S. Pat. No. 3,137,922 shows a method of manufacturing such a product incorporating transverse indentations in the form of an elongated diamond. In this process, the sheet metal strip was first of all passed through a series of roll forming dies or so called "stands" to form longitudingal channel like formations along either edge of the strip, after which the strip was passed through a group of cold working rolls, to flex and extend a portion of the central web of the strip, and then the strip was passed through one pair of embossing rolls. In practice, however, this process was found to produce uneven indentations, with irregular folds or ridges in the metal which did not conform accurately to the shape of the embossing rolls. As a result, the line was difficult to run, and the end product was possessed of uneven and unpredictable stress properties such that it could not in practice be relied upon with any accuracy.
U.S. Pat. No. 3,394,573, granted to E. R. Bodnar, shows a process of embossing transverse indentations without any previous cold working step. Again, while this line was found to be satisfactory for producing relatively simple sections, where both the transverse and the longitudinal indentations were more or less the same depth, it was not found to be entirely satisfactory for producing more complex formations. In addition, while the foregoing proposals describe systems capable of producing a metal strip with continuous deformations formed therein, they were not capable of producing intermittent lengths of such material with indentations formed in some parts, and not in others, and accordingly the usefulness of the earlier systems was somewhat restricted.